In portable battery-operated products, such as selective call receivers, it is a continuing challenge to reduce the drain of current from the battery which powers the receiver. Many efforts have been made to prolong the useful life of a battery, and these efforts are the subject of various patents. See, for example, U.S. Pat. No. 5,251,325 to Davis et al. and 5,150,361 to Wieczorek et al.
Certain portable receivers utilize synthesized receiver circuitry, which suffer from high current drain when operative. It is therefore imperative that the receiver circuitry, particularly those receiver circuitry components which are the greatest load on the battery, be kept powered down as much as possible.
Many battery saving efforts involve powering up the receiver only at times when the device is designated to receive information. At substantially all other times, the receiver is powered down. For the receiver circuitry to be operative at these designated periods of time, the circuitry must be powered up before the necessary time period to be operable to detect and process information. In current implementations, such as for a portable receiver operating on a signaling protocol such as POCSAG (Post Office Code Standardisation Advisory Group), the receiver circuitry is powered up before the designated time slot by a time period corresponding to the worst case warm-up time. This warm-up time may be as much as 40% longer than what is necessary under the best conditions. Warming up the receiver circuitry too early wastes battery power because the circuitry will be operative longer than needed before the designated time slot.
The actual warm-up time of the receiver circuitry varies with temperature and other parameters. It would therefore be desirable to adjust for the changing warm-up time to use battery power more efficiently.